The present invention relates to a composition comprising at least two incompatible thermoplastic polymers and at least one compatibilizer, to a method of preparing this composition, and to the use of said composition for the manufacture of thermoplastic articles or semi-finished products having, in particular, improved mechanical properties.
In general, compositions or blends of polymers meet the requirement of having a set of properties that would be difficult or impossible to obtain with a single polymer. This usually applies to specific properties, such as solvent resistance, impact strength, rigidity, ductility, “barrier”-type properties, abrasion resistance, fire resistance, gloss, etc. Polymer blends may also meet the requirement of providing a lower manufacturing cost, by the addition of a low-cost polymer acting as diluent, and of improving the processibility and/or recyclability.
These polymer compositions are limited by the fact that they include polymers that are generally immiscible—typically being polar and apolar—and consequently require the incorporation of a compatibilizer (the reader may refer to the work by S. M. Krause “Compatible Polymers” in Polymer Handbook, J. Brandrup and E. H. Immergut, Editors, 3rd Edition, Wiley, New York, 1989). Such compatibilization is intended to improve the properties of the composition by reducing the interfacial tension and by improving the adhesion between the phases.
Various compatibilization techniques are used at the present time in compositions based on immiscible polymers:                the addition of a small quantity (with a mass fraction typically ranging from 0.5% to 1%) of a cosolvent compatible with both polymers;        the addition, with a mass fraction substantially between 1% and 20%, of a copolymer of the diblock or triblock type, having two blocks compatible with the two polymers respectively, a triblock copolymer improving the mechanical properties of the composition appreciably more than a diblock copolymer;        the addition of a precrosslinked polymeric modifier of the core-shell type (e.g. of the ethylene/acrylate/maleic anhydride type or glycidyl methacrylate/ethylene/vinyl acetate type) with a higher mass fraction, usually between 20% and 35%, core-shell modifiers being indicated in the case of brittle blends so as to increase the impact strength; and        the in situ generation of a compatibilizer, using the technique known as “reactive compatibilization”, which generates a large interphase and makes it possible to retain the mechanical properties of the blends during particularly demanding conversion processes such as injection moulding (high pressure and high shear).        
Patent document U.S. Pat. No. 6,887,940 itself discloses, in a composition comprising polar and apolar polymers consisting of a polyamide and a polyolefin respectively, the use of a compatibilizer consisting of a polyolefin having carboxylic acid groups formed by prior oxidation.
The advantages of these techniques are well known and indicated in the literature, such as for example in the article by A. Ajji and L. A. Utracki, Polym. Eng. Sci., 36, 1574, (1996)
These techniques make it possible to lower the interfacial tension in polymer blends but they have the major drawback, however, of not giving the composition obtained, on the one hand, satisfactory cohesion and mechanical properties and, on the other hand, a stable morphology after the composition has been processed, for example after injection moulding or extrusion of the composition.
Another drawback of these techniques, such as those consisting of the addition of a core-shell polymeric modifier or of reactive compatibilization, lies in the complexity of their processing.